A method of this type is already known from DE 10 2004 054 711 A1. The known method for operating an internal combustion engine proposes, to increase the accuracy of determining a preferred location of a (crank)shaft of the internal combustion engine, in addition to other measures, filtering a signal characteristic of the combustion process, for example a cylinder pressure signal, in particular by means of a low-pass filter, in order to remove higher-frequency disturbances from the signal.
Whereas, in the past, cylinder pressure sensors have been used virtually solely for research and development purposes in engine development, marked tendencies toward a series use of this component have recently been shown. This applies both to gasoline and to diesel engines. The objective, in addition to dispensing with conventional sensors, such as, for example, the knock sensor, is to have an improved check of the combustion process in order to increase engine efficiency and to adhere to the increasingly stringent statutory emission limit values.
Special mention may be made, in this context, of what is known as the CAI method (controlled auto ignition). This is a homogeneous lean compression ignition method which, because of its sensitivity, is controlled reliably only by the use of cylinder pressure sensors. The cylinder pressure signal in this case serves for determining characteristic combustion process variables, such as the indicated mean pressure and the combustion center of gravity.
The recent processes for controlling an internal combustion engine place high requirements on the exactness of the cylinder pressure data. Experience shows, however, that untreated cylinder pressure signals which are picked up on internal combustion engines are exposed to numerous disturbances even in the case of optimally functioning cylinder pressure sensors. In this case, what is first to be considered is mechanical disturbing influences which originate particularly from the solid-borne sound oscillations of the gas exchange valves which impinge harshly when they close. In addition, there are various types of rapid thermal and electromagnetic disturbing influences which in each case arise at specific time points in the operating cycle of the internal combustion engine and in each case exert a characteristic disturbing influence on the cylinder pressure signal. The problem is, above all, the diversity of the disturbing influences and their high time variability dependent on the rotational speed.